Solenoid operated microburette



Jan. 19, 1960 G. M. ASSET ETAL 2,

SOLENOID OPERATED MICROBURETTE Filed March 18, 1959 n INVENTORSGabriel/e Asset Bernard F Mc Namara B; 4 EMM ATTORNEY United StatesPatent Office 2,921,715 Patented Jan. 19, 1960 Namara, Joppa, Md.,assignors to the United States of America as represented by theSecretary of the Army Application March 18, 1559', Serial No; 800,348

(Granted under Title as, US. Code 1952 see. 266) The invention hereindescribed may be manufactured and used by or for the Government of theUnited States of America for governmental purposes without the paymentto us of any royalty thereon.

This invention relates to a microburette for producing droplets ofcontrollable size. It is an improvement on that described by W. R. Lane,Journal of Scientific Instruments, vol. 24, pp. 98-101 (1947). Ourdevice is so coristructed that it may be used to produce either a singledroplet or a continuous series of droplets of substantially the samesize. The size can be accurately controlled.

The drawing is a diagrammatic view of our apparatus.

A fine hypodermic needle 1 about 25 to 27 gauge is attached to the endof a capillary tube 3 and passes vertically through the airfiow block 5.The slip joint 7 of the needle is seated in the block and the point 9 ofthe needle protrudes through a circular aperture 11 about one-half inch.The airflow block provides for a passage of air flow from a solenoidoperated valve 13 through the circular aperture 11 which forms anannular air jet around the needle 1.

The capillary tube 3 has a fine bore of approximately 0.5 mm. andcomprises two vertical arms, a shorter one 15 and a longer one 17connected by a horizontal portion 18. The shorter arm 15 is attached tothe slip joint 7 of needle 1 while the longer arm 17 is sealed inreservoir 19 which holds the liquid 20 from which the droplets areformed. It will be noted that arm 17 extends nearly to the bottom ofreservoir 19 so that its open lower end is below the level of liquid 20.Arm 17 and reservoir 19 are so proportioned that the level of liquid 20is always below the level of tip 9 of needle 1. This prevents siphoning.Inlet 21 of reservoir 19 is connected through a metering valve 23 and apressure regulator 25 to a source of compressed filtered air 26, havinga source pressure of about lbs. per sq. in.

The solenoid valve 13 is also connected through metering valve 27 andpressure control 29 to the source 30 of compressed air which may have apressure of about 30 lbs. per sq. in. Pressure control 29 is adjusted togive a superatmospheric pressure of less than 10 lbs. per sq. in. atsolenoid valve 13, which is quick acting in this pressure range. Thesolenoid 31 which activates valve 13 has a strong spn'ng return 33.Consequently, valve 13 admits a sudden pulse of air to air flow block 5when solenoid 31 is energized and cuts the air flow off sharply whencurrent is discontinued.

The solenoid may be actuated either automatically or manually. Inautomatic operation the solenoid is controlled by a cam-operated switch35, the lever arm of which rises and falls as the follower of cam 37.The periphery of cam 37 is provided with a groove or indentation 39. Thecam is rotated by motor 41. The duration and frequency of the air pulseare determined by the width of groove 39 and the rate of rotation of cam37.

To secure proper control, it is desirable that the width of groove 39 bevariable. To this end, it is desirable that cam 37 be one of the wellknown adjustable split cams which are commonly used in connection withtime switches of various types. Alternatively, the cam may be so mountedas to be readily removed and replaced, or a plurality of cams may bemounted on the motor shaft and the latter made longitudinallyadjustable.

Means are also provided for manual control of the solenoid valve. A key,43, may be used. Alternatively a manually rotated cam may be provided toactuate switch 35.

Regulators 25, 29 provide the basic regulation of the pressure in thereservoir 19 andv at the solenoid valve 13, respectively. Manuallycontrolled metering valves 23, 27 provide for the fine control of thesepressures. The pressures at the various points are indicated by pressuregauges 45 and 47 and by manometer 49, having reservoir 51. Provision ofa small leak 52 permits a slight how of air at all times through valve23 and gives better control of the pressure. By these controls andgauges, it is possible to keep conditions the same from day to day.Electric counter 53 counts the number of pulses delivered by solenoidvalve 13.

Operation Reservoir 19 is filled with liquid 20 to about the depthindicated in the drawing. Pressure is then applied to the reservoir inan amount just sufficient to cause the liquid to flow through thecapillary tube 3 and slowly form a drop at the point 9 of needle 1. Theair pressure in the reservoir is then carefully reduced until no dropsform at the point of the needle but the surface of the liquid is visiblein the lumen of the point. Under these conditions the total pressure onthe surface formed on the lumen of the point and the surface tension arein equilibrium with the forces due to the difierences of the levels ofthe liquid in the two arms, 15, 17 of tube 3 and the air pressure inreservoir 19. With the proper air pressure at solenoid valve 13, and theproper width of the groove 39 of cam 37, rotation of the cam by motor 41causes a pulse of air to flow through air flow block 5 and the circularaperture 11 surrounding the needle 1. This upsets the equilibrium ofpressures on the surface of the liquid at point 9 of the needle. A finefilament is drawn out of the liquid in the air jet and a portion isbroken off and forms a drop. The size of the drop is determined by thepressure on the liquid 21 in reservoir 19, the duration of the air pulseand the volume of the air in the pulse, the latter being governed by thepressure at solenoid valve 13. This mode of operation, i.e., initialadjustment of the pressures until the forces are at equilibrium at thepoint of needle 1, produces the smallest sizes of drops.

To increase the size of the drop, the pressure in reservoir 19 isincreased. The pressure may be made such that a drop grows very slowlyatthe tip of the needle. The air jet blows the drop off the point beforeit falls under its own weight. The drop size is determined by thepressures and the timing of the air pulse. The duration and volume ofthe air pulse must be controlled to prevent scattering of the drop.

The initial determination of the conditions to produce drops of a givensize is made experimentally. Once they are determined, reproducibleresults can be maintained by keeping the same indicated pressures onmanometer 49 and the pressure gauge 47 and the same timing of solenoidvalve 13. The operation of the valve is, in turn,

determined by the speed of motor 41 and the width of groove 39 of cam37.

By the use of a manually controlled switch such as key 43 or the otherarrangements described above single drops can be released. By theautomatic control of the switch, an extended series of drops of uniformsize, uniformly spaced in time, can be produced. By the variasiderablerange in size of drops is possible. We have produced uniform dropssingly and in series in the range 0.500 to 0.130 mm.

We claim: 7 W v V 1. Apparatus for producing droplets of Controllablesize comprising a closed reservoir, a capillary discharge tube having aninlet communicating with said reservoir near the bottom thereof, saiddischarge tube terminating in a downwardly directed fine-bored tip, anair supply tube communicating with said reservoir at a point above saidinlet, whereby said reservoir is adapted. to retain a body of liquidbetween said inlet and said air supply tube, said tip being positionedat ca level, above'that of said airrsupply tube,'first air supply meansadapted to supply air under superatmospheric pressureto said air supplytube, control means associated withsaid first air supply means andadapted to accurately control the pressure of the. air delivered to saidair supply tube an air flow block defining a. downwardly directedaperture surrounding said tip, second air supply means adapted to supplyair under superatmospheric pressure to said air flow block, said secondair supply means comprising a quick' acting solenoid valve "adapted toquickly admit air to said block and then quickly shut oflE said air,control means adapted to deliverjair to said air flow block throughsaid, solenoid valve underaccurately controlled pressure, and electricswitching means adapted to energize said solenoid valve. f

2. Apparatus as defined inclaim 1 wherein said electric switching meanscomprises 'a switch arid a motor driven cam arranged to periodicallyopen and close said switch.

References Cited iri the'fil'of this patent W. R. Lane: IournaljofScientific Instruments, vol. 24, January 1947, pp. 98-1-1, published bythe Institute of Physics, 47 Belgrave Square, London, S. W.l

